#include<fstream.h>
#include<iostream>
using namespace std;
int s=0,n,v[2000000]={1},i;
ofstream out("ciur.out");
ifstream in("ciur.in");
void prim(int d){
	int j;
	for(j=d;j<=n;j=j+d)
		v[j]=0;
}
int main(){
	in>>n;
	for(i=1;i<=n;i++) v[i]=1;
	for(i=2;i<=n;i++)
		if(v[i]==1){
			//out<<s<<v[i]<<endl;
			
			s++;
			prim(i);
		}
	out<<s;
}